The influence of Pt islands on the failure of Pt thin film on a flexible PET substrate

Abstract

Flexible electronic devices must adapt to compliant polymeric substrates, thus maintaining the mechanical integrity of the multilayer systems is crucial. This study investigates the mechanical failure caused by active islands, focusing on how Pt islands influence the failure mechanism of a thin Pt film on a flexible polyethylene terephthalate (PET) substrate under uniaxial tensile loading. Tensile testing of the Pt film/PET bilayer revealed a failure progression in the Pt blanket film, characterized by crack initiation, elongation and merging, eventually delamination, and buckling, with the increase in tensile strain. Pt islands induced early crack initiation at comparatively low strains due to increased stress near their vertical edges. The impact of island shape and gap on the crack formation in a Pt film was subsequently investigated. The gap between islands, oriented perpendicular to the loading direction, has minimal impact on crack number and density; the presence of Pt islands reduced the stress in the Pt film within the gap, thereby lowering the susceptibility of cracking in these areas. Variations in island shape and gap along loading direction alter the stress profile in the film between islands but did not significantly impact crack density. Crack density is believed to be primarily associated with pre-existing defects, with the formation of cracks serving as a stress relief mechanism that prevents further crack initiation. Our study sheds light on the impact of active islands on blanket film failure and offers practical recommendations to mitigate crack formation, which may contribute to the optimisation of flexible electronics design.